Control of a power supply system (voltage control, load flow control, etc.) has been performed in accordance with the process flow diagram of FIG. 6. In step 104, the various on-line data readings, i.e., voltages, power flows, etc., are obtained. In step 106, a proposed control amount, i.e., change in voltage, power injections, etc., is initially established. Then in step 108, load flow calculation is performed to determine the various power flows, voltages and phases that will be produced in the power system if the proposed control adjustment is performed. The results of the load flow calculations 108, are evaluated in step 110, and then in step 112, the program or process branches to either step 114 or step 116 depending upon whether the evaluation determines an acceptable or non-acceptable system. When the power system as determined by the load flow calculation 108 is non-acceptable, step 116 changes the control amount initially set in step 106 or later set in a previous step, and returns to the load flow calculation step 108. When the calculated power system in step 108 becomes acceptable, the step 114 makes the control amount correction to obtain optimum or correct operation of the power system. It is seen that it is necessary to perform the load flow calculation many times and therefore high-speed load flow calculation is necessary to provide corrections to meet changing power system conditions or to correct for an outage or failure.
FIG. 1 shows a flow chart of a load flow calculation by a prior art fast decoupled method as described, for example, in "Fast Decoupled Load Flow, IEEE PAS-93, No. 3, PP 859-867". Referring to the drawing, 1 denotes a block for determining initial values of voltage V and phase .theta. of each bus bar, 2 denotes a block for providing Jacobian matrix J.sub.1 for effective power with respect to phase of the effective power and Jacobian matrix J.sub.4 for reactive power with respect to voltage and making triangular factorization of J.sub.1 and J.sub.4, 3 denotes a block for providing, with V and .theta., effective power flowing in through each node, obtaining the difference .DELTA.P between this value and the specified value of the inflow effective power for each node, and in succession thereto calculating .DELTA.P/V by dividing .DELTA.P for each node by V on each node, 4 denotes a block for deciding convergence, 5 denotes a block for solving a linear equation .DELTA.P/V=J.sub.1 .DELTA..theta. with .DELTA.P/V obtained in the block 3 and the result of the triangular factorization of J.sub.1 obtained in the block 2 thereby to obtain a correction value .DELTA..theta. of the phase, 6 denotes a block for correcting .theta. with .DELTA..theta., 7 denotes a block for providing, with V and .theta., reactive power flowing in through each node, obtaining the difference .DELTA.Q between this value and the specified value of the inflow reactive power for each node, and in succession thereto calculating .DELTA.Q/V by dividing .DELTA.Q for each node by V on each node, 8 denotes a block for deciding convergence, 9 denotes a block for solving a linear equation .DELTA.Q/V=J.sub.4 .DELTA.V with .DELTA.Q/V obtained in the block 7 and the result of the triangular factorization of J.sub.4 obtained in the block 2 thereby to obtain a correction value .DELTA.V of the voltage, and 10 denotes a block for correcting V with .DELTA.V.
In the prior art calculating method, it was necessary to make triangular factorization of each of the Jacobian matrixes J.sub.1 and J.sub.4 in the block 2 of FIG. 1 and therefore required large calculating volume.